Heterogeneous catalysts for the oxidative dehydrogenation of alkanes or oxidative coupling of methane

ABSTRACT

Improved methods of oxidative dehydrogenation (ODH) of short chain alkanes or ethylbenzene to the corresponding olefins, and improved methods of oxidative coupling of methane (OCM) to ethylene and/or ethane, are disclosed. The disclosed methods use boron- or nitride-containing catalysts, and result in improved selectivity and/or byproduct profiles than methods using conventional ODH or OCM catalysts.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/993,665 filed on May 31, 2018 and issued as U.S. Pat. No. 10,407,364on Sep. 10, 2019, which is a continuation of U.S. application Ser. No.15/260,649 filed on Sep. 9, 2016 and issued as U.S. Pat. No. 10,011,540on Jul. 3, 2018, which claims the benefit of U.S. provisionalApplication No. 62/215,879 filed on Sep. 9, 2015. Each of theseapplications is incorporated by reference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

N/A

FIELD OF THE INVENTION

The disclosure relates to methods of catalyzing reactions that occurunder oxidative conditions, such as the oxidative dehydrogenation ofalkanes or the oxidative coupling of methane, using a catalystcontaining boron and/or nitride.

BACKGROUND OF THE INVENTION

C₃ and C₄ olefins, such as propylene (propene), 1-butene, isobutene andbutadiene, are widely used starting materials in the industrialsynthesis of a variety of important chemical products. The principalindustrial method for producing C₃ and C₄ olefins is steam cracking, apetrochemical process in which saturated hydrocarbons are broken downinto smaller, often unsaturated, hydrocarbons. The products obtained bysteam cracking depend on the composition of the feed, thehydrocarbon-to-steam ratio, and on the cracking temperature and furnaceresidence time. For example, a feed composition that primarily containsethane (ethane cracking) would result in high ethylene yields, while afeed composition including larger hydrocarbons, such as naptha (napthacracking), would result in a larger yield of C₃ and C₄ olefins.

Over the last decade, the demand for C₃ and C₄ olefins has outstrippedsupply from traditional cracker units, and this trend is expected toaccelerate over the next decade. For example, the current world demandfor propene is around 100 million metric tons per year (MTA), and isexpected to increase significantly over the next five years. This trendis primarily due to the availability of cheap shale gas, prompting manychemical companies to convert their naphtha crackers into ethanecrackers, thus shifting production towards ethylene and away from longerchain C₃ and C₄ olefins. Accordingly, the demand for C₃ and C₄ olefinsis growing faster than can be supplied by only cracking.

Because C₃ and C₄ olefin production by conventional steam cracking hasnot kept pace with rising demand, several alternative “on-purpose”olefin production technologies that convert short chain alkanes to thecorresponding olefins have been developed. Examples include thecatalytic dehydrogenation (DH) of short chain alkanes, such as propane,to the corresponding olefin, such as propene, using a supportedCrO_(x)/Al₂O₃ catalyst (“CATOFIN®” (Lummus)), a Pt/Sn alloy supported onAl₂O₃ (“OLEFLEX™” (UOP)), or Pt/Sn supported on Zn-aluminate with co-fedsteam (“STAR®” (Uhde)) (see Sattler et al., Chem. Rev., 2014, 114 (20),10613-10653).

These and other currently used on-purpose dehydrogenation technologiesare energy intensive, because the dehydrogenation reaction is highlyendothermic. Furthermore, because they require high temperatureconditions, they result in substantial catalyst deactivation due to theformation of coke. Thus, they require continuous catalyst regeneration.In addition, these processes may require substantially reduced pressureto shift the dehydrogenation equilibrium towards the desired products,further contributing to the high production costs associated with thesemethods.

Oxidative dehydrogenation (ODH), the catalytic dehydrogenation offeedstock alkanes in the presence of oxygen, is an intriguingalternative to conventional dehydrogenation that addresses each of thedisadvantages of current DH technology. When oxygen is co-fed to act asa reactant, the reaction thermodynamics are altered such that theresulting net reaction is exothermic. Accordingly, the reaction canproceed at much lower reaction temperatures, resulting in decreasedenergy costs and increased catalyst stability. Oxygen in the feed streamalso eliminates coke formation on the catalyst surface and thus createsno need for catalyst regeneration.

Despite these purported advantages, industrial-scale ODH processes havenot been implemented, due to poor control of unwanted side-reactions(mainly the over-oxidation of olefin to CO and CO₂), which results inlow olefin selectivity at conversions necessary for industrialimplementation. For example, existing catalysts for propane ODHtypically provide ˜50-60% selectivity to propene at 10% propaneconversion, with the byproducts largely made up of CO and CO₂. As aresult, even after more than 30 years of research into catalysisdevelopment for ODH (almost entirely focused on supporting vanadiumoxide on amorphous oxide supports (e.g., SiO₂, Al₂O₃, TiO₂, CeO₂, ZrO₂)and structured oxides (e.g., MCM-41, SBA-15)), ODH has not beensuccessfully used in the industrial-scale production of C₃ and C₄olefins.

Accordingly, there is a need in the art for improved methods andcatalysts for the oxidative dehydrogenation of C₃-C₅ alkanes to thecorresponding olefins.

BRIEF SUMMARY

We disclose herein new and improved methods for catalyzing the oxidativedehydrogenation of C₂-C₅ alkanes or ethylbenzene to the correspondingC₂-C₅ olefins or styrene, as well as improved methods for catalyzing theoxidative coupling of methane to form ethane and/or ethylene. Theimproved methods use catalysts containing boron, nitride, or both, tosubstantially increase selectivity (and productivity) for the desiredolefin reaction product, while greatly decreasing the production ofunwanted byproducts, such as CO and CO₂. In a non-limiting example, useof the disclosed catalyst for ODH of propane to propene (ODHP) provided77% propene selectivity at 17% propane conversion, with the byproductsbeing primarily ethylene, and with negligible CO_(x) formation. Theexemplary catalyst stayed active over 8 days with no need forregeneration treatment, showing a marked improvement in reactivity overthis time period.

Accordingly, the disclosure encompasses a method of making one or moredesired chemical products. The method includes the step of contacting aheterogeneous catalyst comprising boron, nitride, or both, with oxygenand one or more liquid or gaseous reactants. The one or more desiredchemical products are formed by a process catalyzed by the heterogeneouscatalyst. The processes that can be catalyzed by the heterogeneouscatalyst include oxidative dehydrogenation (ODH) or oxidative methanecoupling (also known as oxidative coupling of methane, OCM).

In some embodiments, the process catalyzed by the heterogeneous catalystis not zero order with respect to oxygen.

In some embodiments, the liquid or gaseous reactant is an alkane, theprocess catalyzed by the heterogeneous catalyst is oxidativedehydrogenation, and the one or more desired chemical products areolefins. In some such embodiments, the alkane is a C₃-C₅ alkane,including without limitation a C₃-C₅ n-alkane or iso-alkane. In somesuch embodiments, the alkane is a C₄-C₅ alkane, including withoutlimitation a C₃-C₄ n-alkane or iso-alkane. In some such embodiments, theC₃-C₄ alkane is propane, n-butane, or isobutane, and the one or moredesired chemical products may include propene, isobutene, 1-butene,2-butene, and/or butadiene.

In some embodiments, the liquid or gaseous reactant is a hydrocarboncomprising an alkyl group, the process catalyzed by the heterogeneouscatalyst is oxidative dehydrogenation, and the one or more desiredchemical products include one or more hydrocarbons comprising an alkenylgroup. In some such embodiments, the hydrocarbon comprising an alkylgroup is ethylbenzene, and the one or more desired chemical productsinclude styrene.

In some embodiments, the method maintains a greater than 70% selectivityfor the desired chemical products (e.g., olefins) at 10% to 20%conversion of the alkane. In some such embodiments, the method maintainsa greater than 77% selectivity for the olefin at 10% to 20% conversionof the alkane. In some such embodiments, the method maintains a greaterthan 80% selectivity for the olefin at 10% to 20% conversion of thealkane.

In some embodiments, the alkane is propane and the desired chemicalproducts include propene. In some embodiments, the alkane is n-butaneand the desired chemical products include 1-butene and/or 2-butene. Insome embodiments, the alkane is isobutane and the desired chemicalproducts include isobutene.

In some embodiments, the one or more desired chemical products furtherinclude ethylene. In some such embodiments, the method exhibits a higherselectivity towards ethylene than it does towards undesired CO or CO₂byproducts. In some such embodiments, the method exhibits a 90% orgreater selectivity for the propene, ethylene and other desired products(e.g., other olefins) together.

In some embodiments, the one or more liquid or gaseous reactants includemethane, the heterogeneous catalyst catalyzes oxidative coupling ofmethane, and the one or more desired chemical products include ethaneand/or ethylene. In some such embodiments, the heterogeneous catalyst iscontacted with natural gas.

In some embodiments, the heterogeneous catalyst includes a boron- ornitride-containing compound.

In some embodiments, the heterogeneous catalyst includes anitride-containing compound. In some such embodiments, thenitride-containing compound is B-nitride, Si-nitride, Ti-nitride, orAl-nitride.

In some embodiments, the heterogeneous catalyst includes aboron-containing compound. In some such embodiments, theboron-containing compound B-nitride, B-carbide, Ti-boride, Ni-boride, orNb-boride.

In some embodiments, the boron- or nitride-containing compound is boronnitride. In some such embodiments, the boron nitride has a surface areaof greater than 5 m²g⁻¹, greater than 10 m²g⁻¹, greater than 20 m²g⁻¹,greater than 30 m²g⁻¹, greater than 40 m²g⁻¹, greater than 50 m²g⁻¹,greater than 60 m²g⁻¹, greater than 70 m²g⁻¹, greater than 80 m²g⁻¹,greater than 90 m²g⁻¹, greater than 100 m²g⁻¹, greater than 110 m²g⁻¹,greater than 120 m²g⁻¹, greater than 130 m²g⁻¹, greater than 140 m²g⁻¹,greater than 150 m²g⁻¹, greater than 180 m²g⁻¹, greater than 200 m²g⁻¹,greater than 250 m²g⁻¹, greater than 300 m²g⁻¹, greater than 350 m²g⁻¹,greater than 400 m²g⁻¹, greater than 450 m²g⁻¹, or greater than 500m²g⁻¹. In some such embodiments, the boron nitride has a surface arearange of about 5 m²g⁻¹ to 550 m²g⁻¹, about 9 m²g⁻¹ to 550 m²g⁻¹, about50 m²g⁻¹ to 550 m²g⁻¹, about 100 m²g⁻¹ to 500 m²g⁻¹, or about 100 m²g⁻¹to 200 m²g⁻¹. In certain exemplary embodiments, the boron nitride has asurface area of about 150 m²g⁻¹, about 180 m²g⁻¹, about 200 m² g⁻¹,about 250 m² g⁻¹, about 300 m² g⁻¹, about 350 m² g⁻¹, about 450 m² g⁻¹,or about 500 m²g⁻¹.

In some embodiments, the boron nitride is in the form of hexagonal boronnitride (h-BN), boron nitride nanotubes (BNNTs), boron nitridenanosheets (BNNSs), boron nitride nanoribbons (BNNRs) or boron nitridenanomeshes (h-BN nanomeshes).

In some embodiments, the boron nitride further includes oxygen atoms. Insome such embodiments, the oxygen atoms are covalently bonded to boron,nitrogen, and/or other oxygen atoms. In some embodiments, the oxygenatoms may be bonded (functionalized) to the surface of the boronnitride.

In some embodiments, the heterogeneous catalyst comprises an oxynitride.

In some embodiments, the heterogenous catalyst is not simultaneouslycontacted with nitrogen.

In some embodiments, the oxygen and one or more liquid or gaseousreactants are in a reactant stream that is contacted with theheterogeneous catalyst. In some such embodiments, the reactant streamincludes from 0% to 70% nitrogen by volume.

Further objects, features and advantages of the invention will beapparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be better understood and features, aspects andadvantages other than those set forth above will become apparent whenconsideration is given to the following detailed description thereof.Such detailed description makes reference to the following drawings.

FIG. 1 is a graph showing selectivity to propene plotted against propaneconversion for ODHP using boron nitride (BN) and conventional catalysts.The BN catalyst shows much more stable propene selectivity withincreasing propane conversion than the more traditional vanadium oxidecatalyst supported on SiO₂ (V/SiO₂) or SBA-15 (V/SBA-15).

FIG. 2 is a graph showing the relationship between product selectivitiesand propane conversion percentages when using vanadium oxide supportedon SiO₂ (V/SiO₂) or the BN catalyst. Product selectivities arerepresented by the bar plots and are shown on the left-axis, whilepropane conversions are represented by the black diamonds and are shownon the right-axis.

FIG. 3 is a graph showing the results of a long-term stability testcompleted using the BN catalyst to look for any indication of catalystdeactivation. Propane conversion and propene yield (filled-black squareand open-black square, respectively) are shown on the left-axis, whilepropene selectivity (circle) is shown on the right-axis.

FIG. 4 is a graph showing high propene selectivity at relatively highpropane conversions with the use of the BN catalyst, confirmed from BNprovided by two separate chemical suppliers.

FIG. 5 is a graph showing product selectivities and propane conversionpercentages using various boron- or nitride-containing catalysts thatwere screened for oxidative dehydrogenation of propane (ODHP). Productselectivities are represented by the bar plots and are shown on theleft-axis, while propane conversion percentages are represented by theblack diamonds and are shown on the right-axis.

FIG. 6 is a graph showing selectivity to propene plotted against propaneconversion for ODHP using a variety of catalysts. Both boron- andnitride-containing catalysts show activity for ODHP.

FIG. 7A is a graph showing selectivity to propene plotted againstpropane conversion for ODHP, comparing previously reported data fromrepresentative catalysts to hexagonal boron nitride (h-BN) and boronnitride nanotubes (BNNT). Open shapes indicate data from other works,cited within the FIG. (1-7; 1: B. Frank, A. Dinse, O. Ovsitser, E. V.Kondratenko, R. Schomaecker, Appl. Catal. A: Gen., 323, 66-76 (2007); 2:C. L. Pieck, M. A. Banares, J. L. G. Fierro, J. Catal., 224, 1-7 (2004);3: A. Christodoulakis, M. Machli, A. A. Lemonidou, S. Boghosian, J.Catal., 222, 293-306 (2004); 4: P. Viparelli, P. Ciambelli, L. Lisi, G.Ruoppolo, G. Russo, J. C. Volta, Appl. Catal. A: Gen., 184, 291-301(1999); 5: C. Carrero, M. Kauer, A. Dinse, T. Wolfram, N. Hamilton, A.Trunschke, R. Schlogl, R. Schomaecker, Catal. Sci. Technol., 4, 786-794(2014); 6: E. V. Kondratenko, M. Cherian, M. Baerns, D. Su, R. Schlogl,X. Wang, I. E. Wachs, J. Catal., 234, 131-142 (2005); 7: B. Frank, J.Zhang, R. Blume, R. Schogl, D. S. Su, Angew. Chem. Int. Ed., 48,6913-6917 (2009)). Gas contact times (WHSV⁻¹) are varied to achieve arange of conversions and differs depending on the reactivity of thematerial; V/SiO₂: 5-15 kg-cat s mol C₃H₈ ⁻¹; h-BN: 15-40; BNNT: 2-5;T=490° C., P_(O2)=0.15 atm, P_(C3H8)=0.3 atm.

FIG. 7B is a bar graph showing comparisons of ODHP product selectivityamong V/SiO₂ (X_(C3H8)=5.8%), h-BN (X_(C3H8)=5.4%) and BNNT(X_(C3H8)=6.5%) catalysts. Product selectivity is represented by shadedbars. Gas contact times (WHSV⁻¹) are varied to achieve a range ofconversions and differs depending on the reactivity of the material;V/SiO₂: 5-15 kg-cat s mol C₃H₈ ⁻¹; h-BN: 15-40; BNNT: 2-5; T=490° C.,P_(O2)=0.15 atm, P_(C3H8)=0.3 atm.

FIG. 7C is a graph showing comparisons of ODHP propene productivity(kg-C₃H₆ kg-cat⁻¹ hr⁻¹) plotted as a function of C₃H₈ conversion amongV/SiO₂, h-BN and BNNT catalysts. The great selectivity to propeneafforded by BN materials, coupled with the increased activity of BNNT,leads to superior productivity using BNNT. Gas contact times (WHSV⁻¹)are varied to achieve a range of conversions and differs depending onthe reactivity of the material; V/SiO₂: 5-15 kg-cats mol C₃H₈ ⁻¹; h-BN:15-40; BNNT: 2-5; T=490° C., P_(O2)=0.15 atm, P_(C3H8)=0.3 atm.

FIG. 8 is a graph showing ODHP selectivity to olefins (propene+ethene)(filled shapes), as well as oxygen conversion (open shapes), plottedagainst propane conversion, comparing hexagonal boron nitride (h-BN,square shapes) and boron nitride nanotubes (BNNT, circular shapes). Useof BN materials results in higher olefin selectivity and lowerconsecutive propene over-oxidation (corresponding to the slope of thesecurves) than when using V/SiO₂. Oxygen remains present even at highpropane conversion. Gas contact time with these catalysts variesdepending on the reactivity of the material; h-BN: 15-40 (kg-cat s molC₃H₈ ⁻¹); V/SiO₂: 5-15 (kg-cat s mol C₃H₈ ⁻¹); BNNT: 2-5 (kg-cat s molC₃H₈ ⁻¹); T=490° C., P_(O2)=0.15 atm, P_(C3H8)=0.3 atm (balance N₂).

FIG. 9 is a graph showing ODHP propane conversion and propene yield as afunction of time on stream using h-BN. Propane conversion (filledshapes) and propene yield (open shapes) remain stable for at least 32hours on stream when the experiment was discontinued. T=490° C.,WHSV⁻¹=24 kg-cat s mol C₃H₈ ⁻¹, P_(O2)=0.2 atm, P_(C3H8)=0.3 atm(balance N₂).

FIG. 10 is a graph showing ODHP propane conversion plotted as a functionof inverse-weight-hour-space-velocity (WHSV⁻¹, kg-cat s mol-C₃H₈ ⁻¹),comparing h-BN (lower right line) to BNNT (upper left line) catalysts.The slope of each of these lines indicates the rate of propaneconsumption. Much less BNNT is needed to achieve equivalent conversionswhen using h-BN as a consequence of the superior reactivity of the BNNTmaterial. T=490° C., P_(O2)=0.15 atm, P_(C3H8)=0.3 atm (balance N₂).

FIGS. 11A and 11B are graphs showing rates of ODHP propane consumptionusing h-BN as a function of (11A) P_(O2) (P_(C3H8) constant at 0.3 atm),and (B) P_(C3H8) (P_(O2) constant at 0.2 atm) fit with Eley-Ridealkinetics, showing O₂ adsorption and second-order dependence with respectto P_(C3H8). Solid lines are a least-square fit taking into account allexperimental data points at each respective temperature using the ratelaw displayed in FIG. 11B.

FIG. 12 is a bar graph showing metal impurity analysis of BN materialsfrom various suppliers (Sigma-Aldrich, Alfa-Aesar, and BNNT, LLC), aswell as two batches from Sigma-Aldrich (batch #1: Lot STBF0279V; batch#2: Lot STBF7843V). Additional metals (Ni, Pt, V, Cu, Zr, Ga, Mo, Ag,and Na) were screened, but always registered below the detection limit.

FIG. 13 is a graph showing ODHP propene selectivity plotted as afunction of propane conversion for h-BN supplied by Alfa-Aesar andSigma-Aldrich (batch #1: Lot STBF0279V, circles; batch #2: LotSTBF7843V, triangles) and BNNT (BNNT, LLC, diamonds). Despite slightdifferences in metal impurities between batches and suppliers,selectivity to propene between samples is almost identical (±5%).WHSV⁻¹: 15-40 (kg-cat s mol C₃H₈ ⁻¹) [h-BN]; 2-5 (kg-cat s mol C₃H₈ ⁻¹)[BNNT]; T=490° C., P_(O2)=0.15 atm, P_(C3H8)=0.3 atm (balance N₂).

FIG. 14 is a bar graph showing comparisons of ODHP propane conversion(diamonds, right-axis) and product selectivity (bars, left-axis) amongdifferent BN suppliers (Sigma-Aldrich, Alfa-Aesar, and BNNT, LLC) andbatches of h-BN from Sigma-Aldrich (batch #1: Lot STBF0279V; batch #2:Lot STBF7843V). Despite slight differences in metal impurities betweenbatches and suppliers, product selectivity between samples are almostidentical. WHSV⁻¹: 15-40 (kg-cat s mol C₃H₈ ⁻¹) [h-BN]; 2-5 (kg-cat smol C₃H₈ ⁻¹) [BNNT]; T=490° C., P_(O2)=0.15 atm, P_(C3H8)=0.3 atm(balance N₂).

FIG. 15 is a graph showing that both boron- and nitride-containingcatalysts, including nickel boride (Ni-boride) show activity foroxidative dehydrogenation of propane (ODHP); T=490° C., P_(O2)=0.15 atm,P_(C3H8)=0.3 atm.

FIG. 16 is a graph showing BN nanotube n-butane ODH conversion (blacksquares, right axis) and product selectivity (bars, left axis) as afunction of reaction temperature. C4 selectivity combines selectivity to1-butene and 2-butenes.

FIG. 17 is a graph comparing BN nanotube n-butane ODH conversion(x-axis) and C4 selectivity (y-axis) with reported state of the artcatalysts. p-o-CNT denotes functionalized carbon nanotubes. BNNTs showcomparable selectivity to the most selective catalysts reported. Opensymbols indicate reactivity data from other works, cited within the FIG.1-3; 1: Zhang, J.; Liu, X.; Blume, R.; Zhang, A.; Schlogl, R.; Su, D. S.Science. 2008, 322 (5898), 73-77.; 2: Nieto, J. M. L.; Concepcion, P.;Dejoz, a; Knozinger, H.; Melo, F.; Vazquez, M. I. J. Catal. 2000, 189(1), 147-157.; 3: Madeira, L. M.; Portela, M. F. Catal. Rev. 2002, 44(2), 247-286.).

FIG. 18 is a graph showing comparisons of isobutane conversion(diamonds, right-axis) and product selectivity (bars, left-axis) whenusing vanadium oxide supported on silica (V/SiO₂), hexagonal BN (h-BN),and BN nanotubes (BNNT) as catalysts for ODH of isobutane. BN materialsshow much higher selectivity to olefins than the traditional V/SiO₂catalyst, which shows high selectivity to CO_(x) (˜40%). WHSV⁻¹: 16-48(kg-cat s mol C₄H₁₀ ⁻¹) [V/SiO₂]; 44-111 (kg-cat s mol C₄H₁₀ ⁻¹) [h-BN];4-12 (kg-cat s mol C₄H₁₀ ⁻¹) [BNNT]; T=440° C., P_(O2)=0.1 atm,P_(C4H10)=0.1 atm (balance N₂).

FIG. 19 is a graph showing product selectivity (y-axis) plotted againstisobutane conversion (x-axis) when using vanadium oxide supported onsilica (V/SiO₂), hexagonal BN (h-BN), and BN nanotubes (BNNT) ascatalysts for ODH of isobutane. WHSV-1: 16-48 (kg-cat s mol C₄H₁₀ ⁻¹)[V/SiO₂]; 44-111 (kg-cat s mol C₄H₁₀ ⁻¹) [h-BN]; 4-12 (kg-cat s molC₄H₁₀ ⁻¹) [BNNT]; T=440° C., P_(O2)=0.1 atm, P_(C4H10)=0.1 atm (balanceN₂).

FIG. 20 is a graph showing propane consumption when using untreated h-BN(hBN) and oxygen functionalized h-BN (hBN_HNO₃) as ODHP catalysts.Oxygen functionalized h-BN shows ˜40% higher rate of propane consumptionas compared to untreated h-BN.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION I. In General

Before the present materials and methods are described, it is understoodthat this invention is not limited to the particular methodology,protocols, materials, and reagents described, as these may vary. It isalso to be understood that the terminology used in this disclosure isfor the purpose of describing particular embodiments only, and is notintended to limit the scope of the present invention, which will belimited only by the language of the appended claims.

As used in this disclosure and in the appended claims, the singularforms “a”, “an”, and “the” include plural reference unless the contextclearly dictates otherwise. The terms “a” (or “an”), “one or more” and“at least one” can be used interchangeably. The terms “comprising”,“including”, and “having” can also be used interchangeably.

Unless defined otherwise, all technical and scientific terms used inthis disclosure, including element symbols, have the same meanings ascommonly understood by one of ordinary skill in the art. Chemicalcompound names that are commonly used and recognized in the art are usedinterchangeably with the equivalent IUPAC name. For example, ethene isthe same as ethylene, propene is the same as propylene, butene is thesame as butylene, 2-methylpropane is the same as isobutane, and2-methylpropene is the same as isobutene.

The following abbreviations are used throughout this disclosure: BN,boron nitride; BN nanomesh(es), boron nitride nanomesh(es); BNNS(s),boron nitride nanosheet(s), BNNR(s), boron nitride nanoribbon(s);BNNT(s), boron nitride nanotube(s); DH, dehydrogenation; h-BN, hexagonalform of boron nitride; OCM, oxidative coupling of methane; ODH,oxidative dehydrogenation; ODHP, oxidative dehydrogenation of propane;P, partial pressure for a given gas; S, selectivity for a given product;WHSV⁻¹, inverse weight-hour-space-velocity; % X, conversion for a givenreactant.

All publications and patents specifically mentioned in this disclosureare incorporated by reference for all purposes, including for describingand disclosing the chemicals, instruments, statistical analysis andmethodologies that are reported in the publications that might be usedin connection with the disclosed methods and devices. All referencescited in this disclosure are to be taken as indicative of the level ofskill in the art.

II. The Invention

This disclosure is based on our discovery that the use of a boron- ornitride-containing catalyst facilitates improved oxidativedehydrogenation of alkanes, such as propane, to desired olefins, such aspropene. Specifically, the disclosed methods exhibit increasedselectivity towards the desired product while decreasing the productionof unwanted byproducts, such as CO and CO₂. Furthermore, the processoccurs at relatively low temperatures, and the catalyst is stable overtime, and so does not need to be frequently regenerated. The catalystscan also be used for oxidative coupling of methane to produce ethaneand/or ethylene.

Exemplary Forms of Boron Nitride

Boron nitride (BN) is a non-limiting example of a boron- ornitride-containing catalyst that can be used in the disclosed methods.The boron nitride catalyst can be made from any available form of boronnitride, including, without limitation, amorphous boron nitride (a-BN),hexagonal boron nitride (h-BN), cubic boron nitride (c-BN), wurtziteboron nitride (w-BN), boron nitride-containing composites, boron nitridenanotubes (BNNTs), boron nitride nanosheets (BNNSs), boron nitridenanoribbons (BNNRs) and boron nitride nanomeshes.

h-BN, a stable crystal form of BN, has a layered structure similar tographite. Within each layer, boron and nitrogen atoms are bound bystrong covalent bonds, whereas the layers are held together by weak vander Waals forces.

As shown in more detail in the examples below, we have determined thatthe catalytic activity of BN may be enhanced by increasing the surfacearea of the BN. Accordingly, forms of BN exhibiting increased surfacearea, such as boron nitride nanotubes and boron nitride nanomeshes, aresuitable for use in the disclosed methods.

Boron nitride nanotube(s) (BNNT(s)) are cylindrical structures formedfrom “rolled up” sheets of alternating and covalently bonded nitrogenand boron atoms. Typical BNNTs have a diameter of several to hundreds ofnanometers and a length of many micrometers. They are structurallysimilar to carbon nanotubes, which are made up of “rolled up” graphiticcarbon sheets.

Boron nitride nanomesh(es) are two-dimensional boron nitridenanostructures consisting of a single layer of alternating andcovalently bonded boron and nitrogen atoms, which self-assemble to forma highly regular mesh. The structure of BN nanomeshes is similar to thestructure of graphene, in that they form an assembly of hexagonal pores.In a non-limiting example, the distance between two pore centers is 3.2nm and the pore diameter is ˜2 nm, and the pores are about 0.05 nm deep.Other terms used in the literature for this form of boron nitrideinclude h-BN monolayers, boronitrene, white graphene, boron nitridenanosheets, boron nitride nanoribbons, and boron nitride nanoplatelets.

For more information regarding BNNTs and BN nanosheets, see, e.g., D.Golberg, Y. Bando, Y. Huang, T. Terao, M. Mitome, C. Tang and C. Zhi,ACS Nano, 4 (6), 2979-2993 (2010).

Oxygen Functionalization of the BN Surface

As shown in more detail in the examples below, we have determined thatthe catalytic activity of BN may be enhanced by functionalizing the BNsurface with oxygen.

The specific method used to functionalize the BN surface with oxygen isnot limited, and may include any of a number of methods known in theart. For example, Liao et al. (Liao, Y. et al., Sci. Rep. 5, 14510; doi:10.1038/srep14510 (2015)), report using silver nanoparticles to oxidizeh-BN, with the duration and temperatures used in the procedure affectingthe atomic percentage of oxygen functionalized onto the BN surface. Manyother methods are known in the art, including the nitric acid treatmentused in Example 9 below.

The following examples are offered for illustrative purposes only, andare not intended to limit the scope of the invention in any way. Indeed,various modifications of the invention in addition to those shown anddescribed herein will become apparent to those skilled in the art fromthe foregoing description and the following Examples and fall within thescope of the appended claims.

III. Examples Example 1 Substantially Improved Product Selectivity forOxidative Dehydrogenation of Propane to Propene Using the BN Catalyst

In this example, we demonstrate that using a boron nitride catalystsubstantially improves the selectivity of oxidative dehydrogenation ofpropane to propene (ODHP), particularly at higher conversions, ascompared to using conventional ODHP catalysts.

Comparative ODHP Results Using Traditional Catalysts and Boron Nitride.ODHP was performed on a gas mixture containing propane (C₃H₈), Oxygen(O₂) and nitrogen (N₂) flowing past the BN catalyst made up of boronnitride, a vanadium oxide catalyst supported on SiO₂ (V/SiO₂), or avanadium oxide catalyst supported on SBA-15 (V/SBA-15). Operatingconditions for both the BN and supported vanadium oxide catalysts wereas follows: P_(O2)=0.15 atm, P_(C3H8)=0.3 atm, P_(N2)=0.55 atm, T=490°C. For BN, 200 mg of BN particles 600-710 μm in size were loaded in a 9mm inner diameter quartz reactor with total inlet flow rates of 40-120mL min⁻¹, equivalent to inverse weight-hour-space-velocity (WHSV⁻¹) inthe range of 100-300 kg-cat s m⁻³. For V/SiO₂, 130 mg V/SiO₂ particles600-710 μm in size (along with 260 mg SiC inert diluent, equivalent insize) were loaded in a 9 mm inner diameter quartz reactor with totalinlet flow rates of 60-140 mL min⁻¹, equivalent to WHSV⁻¹ in the rangeof 55-130 kg-cats m⁻³. All carbon balances close to within ±5%. For eachcatalyst, inlet flowrates of the C₃H₈/O₂/N₂ gas mixture were varied toachieve a range of propane conversions.

Propene selectivity, S, is calculated as follows:

$S = \frac{F_{{C\; 3H\; 6},{out}}}{\sum F_{{carbon}\mspace{14mu}{prod}}}$where  F_(C 3H 6, out) = flow  of  propene  out  of  reactor  (mol  s⁻¹  g-cat⁻¹)F_(carbon  prod) = flow  of  all  carbon  products  out  of  reactor(mol  s⁻¹  g-cat⁻¹)

Propane conversion, X, is calculated as follows:

$X = \frac{\sum F_{{carbon}\mspace{14mu}{prod}}}{F_{{C\; 3H\; 8},{i\; n}}}$where  F_(carbon  prod) = flow  of  all  carbon  products  out  of  reactor(mol  s⁻¹  g-cat⁻¹)F_(C 3H 8, i n) = flow  of  propane  into  the  reactor  (mol  s⁻¹  g-cat⁻¹)

Inverse weight-hour-space-velocity, WHSV⁻¹ (kg-cat s m⁻³), is calculatedas follows:

${WHSV}^{- 1} = {\frac{M_{cat}}{F_{tot}}*60}$where  M_(cat) = mass  of  catalyst  loaded  in  reactor  (mg)F_(tot) = total  flow  of  all  inlet  gasses  (mL  min⁻¹)

As seen in FIG. 1, use of the BN catalyst results in a much more stablepropene selectivity with increasing propane conversion than the moretraditional vanadium oxide catalyst supported on SiO₂ or SBA-15.Specifically, BN maintained 77% propene selectivity with 17% propaneconversion, while even with a modest 13% propane conversion, thevanadium oxide catalyst supported on SBA-15 shows propene selectivity of48%.

As seen in FIG. 2, use of the V/SiO₂ catalyst (diluted with inert SiC)results in a large drop in propene selectivity with only an increase of˜3% in propane conversion. In contrast, the BN catalyst shows a muchmore gradual drop in propene selectivity with increasing propaneconversion, always showing greater selectivity to propene than theV/SiO₂ catalyst, even at ˜17% propane conversion.

We further quantify the specific ODHP byproducts resulting from usingthe V/SiO₂+SiC and BN catalysts, and the results are shown in FIG. 2.When using the BN catalyst, the main byproduct is ethylene, an importantchemical building block itself. In contrast, when using the V/SiO₂catalyst, the primary byproducts are CO and CO₂. This indicates that BNcatalyzes a drastically different mechanism of propene formation thanV/SiO₂.

In sum, this example demonstrates that improved selectivities andbyproduct mix can be obtained by using boron nitride to catalyze ODH ofshort chain alkanes to the corresponding olefin, in place of traditionalvanadium oxide or other known catalysts.

Example 2 The BN Catalyst is Stable Over the Long Term

A long term stability test was completed using the BN catalyst to lookfor any indication of catalyst deactivation, and the results arereported in FIG. 3. Operating conditions were as follows: P_(O2)=0.3atm, P_(C3H8)=0.3 atm, P_(N2)=0.4 atm, T=490° C. All carbon balancesclose to within ±5%. Testing proceeded for 8.0 day on stream timeperiod.

Referring to FIG. 3, propane conversion and propene yield are shown as afunction of time on stream, and the WHSV during various on stream timeperiods is indicated. After ˜1.5 days on stream, propane conversionbegan to increase, along with the natural decrease in propeneselectivity, indicating that the BN catalyst was becoming more active.This was likely due to the formation of additional active sites. Totalinlet flowrates were then increased from 40 to 50 mL min⁻¹ after 4 dayson stream to decrease WHSV⁻¹ from 294 to 234 kg-cat s m⁻³, in order tobring the propane conversion back to its initial value. After anadditional day, total flow rate was again increased (56 mL min⁻¹) todrop WHSV⁻¹ to 210 kg-cat s m⁻³. Propane conversion again increasedafter several more days, suggesting the continual generation ofadditional active sites.

These results demonstrate that the BN catalyst is stable when usedcontinuously for oxidative dehydrogenation over extended periods oftime. Accordingly, the disclosed method is suitable for cost-efficientindustrial-scale use.

Example 3 ODHP Catalyzed by Boron Nitride from Multiple SourcesDemonstrates Improved Propene Selectivity, with Greater BN Surface AreaFacilitating Higher Conversion Rates

In this example, we demonstrate that boron nitride from two differentsources catalyzed ODHP with improved selectivity for propene atrelatively high conversions. Further analysis revealed that reactivityof BN for ODHP may be proportional to the surface area of the BNcatalyst.

Operating conditions were as follows: P_(O2)=0.15 atm, P_(C3H8)=0.3 atm,P_(N2)=0.55 atm, T=490° C. 200 mg of BN particles 600-710 μm in sizewere loaded in a 9 mm ID quartz reactor with total inlet flow rates of40-120 mL min⁻¹, equivalent to WHSV⁻¹ of 100-300 kg-cat s m⁻³. Allcarbon balances close to within ±2%. Inlet flowrates of the C₃H₈/O₂/N₂gas mixture were varied to achieve a range of propane conversions.

BN was used from two separate chemical suppliers: Sigma Aldrich and AlfaAesar. As seen in FIG. 4, the results were assayed separately, andcompared to the results obtained using V/SiO₂. Interestingly, when usingidentical total inlet flowrates (40 mL min⁻¹), equivalent to 300 kg-cats m⁻³, the BN supplied from Sigma Aldrich achieved ˜17% propaneconversion, while the BN supplied from Alfa Aesar only reached ˜10%propane conversion. This is an indication that the BN from Sigma Aldrichis more reactive per unit of mass than that supplied by Alfa Aesar.

Analysis of the surface area of these two materials (BET) revealed thatthe Sigma Aldrich BN had a 1.8 times greater specific surface area thanthe Alfa Aesar BN. Accordingly, the reactivity of BN for oxidativepropane dehydrogenation may be proportional to the BN surface area, andtherefore could be improved with the synthesis of higher surface area BNmaterials.

Example 4 Other Boron- or Nitride-Containing Compounds are ActiveCatalysts for ODHP, with Boron-Containing Compounds Facilitating HighPropene Selectivity and Improved Byproduct Mix

In this example, we extended the ODHP catalyst assays disclosed in theprevious examples using BN to a range of additional boron- andnitride-containing compounds. The results show that, in general, likeBN, boron- and nitride-containing compounds can catalyze ODHP (andlikely related ODH of short chain alkanes to corresponding olefins).Furthermore, the results show that in general, like BN, boron-containingcompounds catalyze ODHP (and likely related ODH of short chain alkanesto corresponding olefins) with greatly improved selectivity for propeneand improved byproduct mix.

Various boron- or nitride-containing catalysts were screened foroxidative propane dehydrogenation (ODHP), including B-nitride,Si-nitride, Ti-nitride, Al-nitride, B-carbide, Ti-boride, and Nb-boride.FIG. 5 shows product selectivities of the screened catalysts as afunction of propane conversion, and also includes the corresponding datafor the conventional V/SiO₂ catalyst. Operating conditions were asfollows: P_(O2)=0.15 atm, P_(C3H8)=0.3 atm, P_(N2)=0.55 atm, T=490° C.Due to differences in the reactivity between catalysts, total inlet flowrates between catalysts fluctuated between 40 and 140 mL min⁻¹, in orderto achieve ˜5% propane conversion. About 200 mg of boron- ornitride-containing catalysts 600-710 μm in size were loaded in a 9 mminner diameter quartz reactor. All carbon balances close to within ±2%.

As seen in FIG. 5, all the tested boron- or nitride-containing catalystsshow activity for ODHP. Furthermore, all the tested boron-containingcatalysts (B-nitride, B-carbide, Ti-boride, Nb-boride) display highselectivity to propene, with the primary byproduct being ethylene. Incontrast, nitride-containing catalysts other than BN (Si-, Ti,Al-nitride) show markedly lower selectivity to propene than theboron-containing alternatives, and produce CO₂ and CO as the primarybyproducts.

Inlet flowrates of the C₃H₈/O₂/N₂ gas mixture past the screenedboron-containing, nitride-containing and V/SiO₂ catalysts were thenvaried to achieve a range of propane conversions. Operating conditionswere as follows: P_(O2)=0.15 atm, P_(C3H8)=0.3 atm, P_(N2)=0.55 atm,T=490° C. About 200 mg of boron- or nitride-containing catalysts 600-710μm in size were loaded in a 9 mm inner diameter quartz reactor withtotal inlet flowrates of 40-140 mL min⁻¹, equivalent to WHSV⁻¹ of100-300 kg-cat s m⁻³. All carbon balances close to within ±5%.

As shown in FIG. 6, the boron-containing catalysts maintained highpropene selectivity even at high propane conversions. Nitride-containingcatalysts showed lower selectivity to propene, but in the case of Si-and Ti-nitride, propene selectivity did not decrease with increasingpropane conversion.

In sum, this example demonstrates that a variety of boron- andnitride-containing catalyst can be used to catalyze the oxidativedehydrogenation of short chain alkanes to corresponding olefins.

Example 5 Selective Oxidative Dehydrogenation of Propane to PropeneUsing Boron Nitride Catalysts

In this example, we extend the BN ODH catalyst results disclosed in theprevious examples in several specific ways, while providing additionaldetails. First, we demonstrate that effective ODH catalysts can be madefrom either of two different forms of boron nitride: hexagonal boronnitride (h-BN) or boron nitride nanotubes (BNNTs). BNNT catalystspromote increased propene productivity as compared to h-BN catalysts.Second, we propose a mechanism of action that is consistent with ourdata that is fundamentally different from the mechanism of action forODH using traditional catalysts, such as supported vanadia.

SUMMARY

The exothermic reaction of propane with oxygen to generate propene andwater has the potential to be a game-changing technology in the chemicalindustry. However, even after decades of research, the selectivity topropene remains too low to make the reaction economically attractive.This notoriously low selectivity is due to a fundamental scientificchallenge: the desired olefin is much more reactive than the alkanesubstrate, and is therefore readily oxidized to thermodynamicallyfavored CO₂.

In this example we report that hexagonal boron nitride (h-BN) and boronnitride nanotubes (BNNTs) have unique catalytic properties andfacilitate an unprecedented selectivity to propene. As an example, at14% propane conversion, we obtain a selectivity of 77% towards propeneand 13% towards ethene, another desired alkene. Based on catalyticexperiments, in conjunction with spectroscopic investigations and abinitio modeling, we put forward a mechanistic hypothesis in whichoxygen-terminated armchair BN edges are proposed to be the catalyticactive sites.

Experiments, Results, and Discussion.

Here, we present both hexagonal boron nitride (h-BN) and boron nitridenanotubes (BNNTs) as metal-free materials able to catalyze the ODHPreaction. While graphene and fullerene materials are emerging ascatalysts for partial alkane oxidations (D. R. Dreyer, H. P. Jia, C. W.Bielawski, Angew. Chem., 122, 6965-6968 (2010); J. Zhang, X. Liu, R.Blume, A. Zhang, R. Schlogl, D. S. Su, Science, 322, 73-77 (2008); B.Frank, J. Zhang, R. Blume, R. Schogl, D. S. Su, Angew. Chem. Int. Ed.,48, 6913-6917 (2009)), BN materials, one of the “inorganic analogues” ofgraphene, have yet to be explored in the art for their own catalyticactivity. It is actually remarkable that BN, a material deemed to bevery stable and inert, is catalytically active at all.

A supported vanadia on silica catalyst (V/SiO₂) was used in this work tomake direct comparisons to the catalytic performance of BN. Thesematerials were loaded into a quartz tube reactor heated to 460-500° C.under flowing propane, oxygen and nitrogen as an inert carrier gas.Reaction parameters such as temperature, catalyst mass, total gasflow-rate, and partial pressures of propane (PC₃H₈) and oxygen (PO₂)were varied to observe changes to product distributions by sampling thereactor exhaust stream via online gas chromatography and massspectrometry. Gas contact time with the catalyst is represented in thiswork as the inverse-weight-hour-space-velocity (WHSV⁻¹, [kg-catalyst smol C₃H₈ ⁻¹]), which was varied primarily by altering the total gasflow-rate.

Use of BN materials results in extraordinary selectivity to propene notobserved before under ODHP conditions. For instance, h-BN afforded 77%selectivity to propene at 14% propane conversion (FIG. 7A). Meanwhile,the traditional V/SiO₂ allows for a modest 61% propene selectivity atonly 9% propane conversion (J. T. Grant, C. A. Carrero, A. M. Love, R.Verel, I. Hermans, ACS Catal., 5, 5787-5793 (2015)). The obtainedselectivities using state-of-the-art ODHP catalysts (1-7; 1: B. Frank,A. Dinse, O. Ovsitser, E. V. Kondratenko, R. Schomaecker, Appl. Catal.A: Gen., 323, 66-76 (2007); 2: C. L. Pieck, M. A. Banares, J. L. G.Fierro, J. Catal., 224, 1-7 (2004); 3: A. Christodoulakis, M. Machli, A.A. Lemonidou, S. Boghosian, J. Catal., 222, 293-306 (2004); 4: P.Viparelli, P. Ciambelli, L. Lisi, G. Ruoppolo, G. Russo, J. C. Volta,Appl. Catal. A: Gen., 184, 291-301 (1999); 5: C. Carrero, M. Kauer, A.Dinse, T. Wolfram, N. Hamilton, A. Trunschke, R. Schlogl, R.Schomaecker, Catal. Sci. Technol., 4, 786-794 (2014); 6: E. V.Kondratenko, M. Cherian, M. Baerns, D. Su, R. Schlogl, X. Wang, I. E.Wachs, J. Catal., 234, 131-142 (2005); 7: B. Frank, J. Zhang, R. Blume,R. Schogl, D. S. Su, Angew. Chem. Int. Ed., 48, 6913-6917 (2009)) arecompared in FIG. 7A. The decrease in propene selectivity with increasingpropane conversion is indicative of the facile over-oxidation of propeneto CO_(x).

The entire product distribution further distinguishes boron nitridematerials from supported vanadia catalysts (FIG. 7B). When using thesupported vanadia catalyst the main byproducts are COx, accounting for33% of total product selectivity at 9% propane conversion. Conversely,when using BN materials, the main byproduct is ethene, a highly valuableolefin itself, rather than COx. The combined propene and etheneselectivity is 90% at 14% propane conversion using h-BN (FIG. 8). Wefurthermore verified that the catalytic activity of the BN materialremains stable for at least 32 hours on stream (FIG. 9), validating thecatalyst stability.

The analogous product distributions for both h-BN and BNNTs suggest asimilar reaction mechanism for these BN materials. However, BNNTsexhibit a rate of propane consumption [mol C₃H₈ kg-cat⁻¹ s⁻¹] more thanone order-of-magnitude higher than observed with h-BN (FIG. 10). Thehigher activity of BNNTs at least partially reflects the higher surfacearea of BNNTs relative to h-BN (BNNT: 97±5 m² g⁻¹ versus h-BN: 16±1 m²g⁻¹) (J. Kibsgaard, Z. Chen, B. N. Reinecke, T. F. Jaramillo, Nat.Mater., 11, 963-969 (2012)); however, the rate of propane consumption ismore than three times higher with BNNT than with h-BN when normalizedfor surface area (BNNT: 3.6×10⁻⁷ mol C₃H₈ s⁻¹ m⁻² versus h-BN: 1.1×10⁻⁷mol C₃H₈ s⁻¹ m⁻²). This high reactivity and selectivity with BNNTsresults in a substantial enhancement in the observed propeneproductivity [kg-C₃H₆ kg-cat⁻¹ hr⁻¹] (FIG. 7C), comparable to valuesdeemed attractive for commercial implementation of this “on-purpose”propene technology (C. Carrero, M. Kauer, A. Dinse, T. Wolfram, N.Hamilton, A. Trunschke, R. Schlogl, R. Schomaecker, Catal. Sci.Technol., 4, 786-794 (2014); F. Cavani, N. Ballarini, A. Cericola,Catal. Today, 127, 113-131 (2007)).

Further kinetic insights were obtained by studying the influence ofreactant concentrations (P_(O2), P_(C3H8)) on the reaction rate. Theinclusion of oxygen as a reactant is required for propane conversionusing BN materials. The rate of propane consumption using h-BN indicatesoxygen activation on the BN surface (FIG. 11A) and second-orderdependence with respect to P_(C3H8) (FIG. 11B). This kinetic behaviorclearly distinguishes boron nitride from traditional supported vanadiacatalysts, which follow a Mars van Krevelen mechanism (rate-determiningsubstrate oxidation, followed by fast re-oxidation of the surface byoxygen) that typically leads to zero-order rate dependence with respectto P_(O2) and first order in propane (K. Chen, A. Khodakov, J. Yang, A.T. Bell, E. Iglesia, J. Catal., 186, 325-333 (1999)).

It is surprising that BN, a material known for its high stability underoxidative conditions (Z. Liu, Y. Gong, W. Zhou, L. Ma, J. Yu, J. C.Idrobo, J. Jung, A. H. MacDonald, R. Vajtai, J. Lou, P. M. Ajayan, Nat.Commun., 4, 2541 (2013); Y. Chen, J. Zou, S. J. Campbell, G. L. Caer,Appl. Phys. Lett., 84, 2430-2432 (2004)), is catalytically active atall. So far it has been explored for its unique electronic,thermoelectric and mechanical properties (Y. Lin, J. W. Connell,Nanoscale, 4, 6908-6939 (2012); N. G. Chopra, R. J. Luyken, K. Cherrey,V. H. Crespi, M. L. Cohen, S. G. Louie, A. Zettl, Science, 269, 966-967(1995); A. Pakdel, Y. Bando, D. Golberg, Chem. Soc. Rev., 43, 934-959(2014); A. L. Bezanilla, J. Huang, H. Terrones, B. G. Sumpter, J. Phys.Chem. C, 116, 15675-15681 (2012)). The combination of the interestingobservations outlined in this example (i.e. improved selectivity toolefins and different reaction kinetics) points towards a novel,fundamentally different reaction mechanism compared to other,well-studied catalysts. Metal impurities in the material are unlikely toplay a significant role. Indeed, various boron nitride samples fromvarious suppliers, containing different impurities (FIG. 12) show almostidentical catalytic performance (FIGS. 13-14).

Based on semiconductor literature focusing on oxygen-terminated armchairedges of BN (A. L. Bezanilla, J. Huang, H. Terrones, B. G. Sumpter, J.Phys. Chem. C, 116, 15675-15681 (2012)), as well as the proposed activesites of graphene and fullerene materials for other oxidations (J.Zhang, X. Liu, R. Blume, A. Zhang, R. Schlogl, D. S. Su, Science, 322,73-77 (2008); B. Frank, J. Zhang, R. Blume, R. Schogl, D. S. Su, Angew.Chem. Int. Ed., 48, 6913-6917 (2009)), we propose an oxygen-terminatedarmchair edge of BN (>B—O—O—N<) as the active site for the ODHPreaction. In line with the observed oxygen-dependence of the kinetics,we propose that an oxygen molecule bonded to one B and one N atom actsas the active site. These >B—O—O—N< sites can be viewed as inorganicperoxide species, able to perform oxidation reactions.

The second order rate dependence with respect to P_(C3H8) suggests thattwo propane molecules are required to generate two molecules of water,in line with the overall stoichiometry of the reaction. The desorptionof these water molecules forms BN edge vacancies allowing for unique O₂activation, explaining the influence that the surface coverage ofadsorbed oxygen has on the rate of propane consumption.

In summary, this example identifies boron nitride, typically assumed tobe inert, as a hitherto unexplored oxidation catalyst. Exceptionalselectivity towards propene was obtained during the oxidativedehydrogenation of propane.

Materials and Methods.

Hexagonal boron nitride (h-BN, Sigma-Aldrich & Alfa-Aesar) and boronnitride nanotubes (BNNT, BNNT, LLC) were used as provided withoutfurther chemical or thermal treatment. Multiple h-BN batches andsuppliers were used to ensure reproducibility, and to confirm that it istruly the BN material responsible for catalysis, rather than a potentialmetal impurity. All suppliers guarantee >99% purity of h-BN and BNNT,which is confirmed with our own metal impurity analysis using inducedcoupled plasma optical emission spectroscopy (ICP-OES) (FIG. 12).

Acid digestion of BN materials was completed by refluxing ˜10 mg BN in 6mL aqua regia solution (3:1 HCl:HNO₃) overnight, followed by gravityfiltration and dilution of collected acid with 34 mL H₂O (18 MΩ). Thecollected solution was then analyzed using an Optima 2000 DV opticalemission spectrometer (Perkin Elmer Instruments), screening for metalsincluding Fe, Ca, Al, Ti, Ni, Pt, V, Cu, Zr, Ga, Mo, Ag, and Na. Whilethe quantity of metal impurities in h-BN samples vary among batches andsuppliers, the catalytic response between them does not (FIGS. 13-14),ensuring the trace metal impurities do not influence the catalysissignificantly.

The supported vanadia on silica catalyst (V/SiO₂, 4.5 wt % vanadium) wasprepared using well described incipient wetness impregnation procedures,involving the introduction of vanadium oxytriisopropoxide(Sigma-Aldrich) diluted in isopropanol (Sigma-Aldrich) to the SiO₂(Aerosil200, Evonik) surface with subsequent calcination at 550° C. Thevolume of the vanadium oxytriisopropoxide/isopropanol solution wasequivalent to the pore volume of the SiO₂. Raman spectroscopy was usedto ensure two-dimensional dispersion of surface vanadia species, whichallows considerably higher selectivity to propene than materialcontaining three-dimensional V₂O₅ nanoparticles.

Powder h-BN and V/SiO₂ catalysts were compressed using a pellet press(Pike Technologies) and sieved to collect particles of 600-710 μmdiameter in order to limit any potential mass transfer effects. About150 mg V/SiO₂ and 300 mg inert SiC particles (thermal conductor) wereloaded into a quartz reactor tube (9 mm diameter), while about 300 mgh-BN was loaded into the reactor tube without SiC. About 40 mg BNNT(un-pressed) was diluted with about 100 mg inert SiO₂ particles toensure a uniform bed. Flowrates of propane (industrial grade, Airgas),oxygen (UHP, Airgas) and nitrogen (UHP, Airgas) were controlled usingthree mass flow controllers (Bronkhorst) and calibrated to eachindividual gas to allow total flowrates of 40-160 mL min-1. The reactortube was loaded into a Microactivity-Effi reactor setup, which includeda tube furnace capable of maintaining temperatures up to 1100° C. and aliquid-gas separator to condense formed water. The reactor effluent wasanalyzed using a Shimadzu 2010 GC equipped with three Restek columns(Rtx-1, RT-Msieve 5A, and Rt-Q-Bond) and a thermal conductivity detector(TCD) as well as a flame ionization detector (FID). The carbon balanceof each data point closes within 2%.

Equations.

Propane conversion, X, is calculated as follows:

$X = \frac{\sum F_{{carbon}\mspace{14mu}{prod}}}{F_{{C\; 3H\; 8},{i\; n}}}$where  F_(carbon  prod) = flow  of  all  carbon  products  out  of  reactor(mol  s⁻¹  g-cat⁻¹)F_(C 3H 8, i n) = flow  of  propane  into  the  reactor  (mol  s⁻¹  g-cat⁻¹)

Product selectivity, S, is calculated as follows:

$S = \frac{F_{A,{out}}}{\sum F_{{carbon}\mspace{14mu}{prod}}}$where  F_(A, out) = flow  of  carbon  in  product  A  out  of  reactor(mol  s⁻¹  g-cat⁻¹)F_(carbon  prod) = flow  of  all  carbon  products  out  of  reactor(mol  s⁻¹  g-cat⁻¹)

Inverse weight-hour-space-velocity, WHSV⁻¹ (kg-cat s mol C₃H₈ ⁻¹), iscalculated as follows:

${WHSV}^{- 1} = \frac{M_{cat}*\left( {V/n} \right)_{STP}}{F_{total}*N_{C\; 3H\; 8}}$where  M_(cat) = mass  of  catalyst  loaded  in  reactor  (kg)(V/n) = 24.5(L/mol)  at  298.15  K(1  atm, R = 8.206 * 10⁻²  L  atm  K⁻¹  mol⁻¹)F_(tot) = total  flow  of  all  inlet  gasses  (L  s⁻¹)N_(C 3H 8) = mol  percent  propane  in  gas  feed  (mol  %)

Example 6 Nickel Boride as an Additional Active Catalysts for ODHP

In this example, we extend the ODHP catalyst assays disclosed in Example4 to further include Ni-boride. As outlined in Example 4, various boron-or nitride-containing catalysts were screened for oxidative propanedehydrogenation (ODHP) activity, including B-nitride, Ti-nitride,Al-nitride, B-carbide, Ti-boride, and Nb-boride. In this example, wealso demonstrate the catalytic activity of Ni-boride activity.

Operating conditions were as follows: P_(O2)=0.15 atm, P_(C3H8)=0.3 atm,P_(N2)=0.55 atm, T=490° C. Due to differences in the reactivity betweencatalysts, total inlet flow rates between catalysts fluctuated between40 and 140 mL min⁻¹, in order to achieve ˜5% propane conversion. About200 mg of boron- or nitride-containing catalysts 600-710 μm in size wereloaded in a 9 mm inner diameter quartz reactor. All carbon balancesclose to within ±5%.

All the tested boron- or nitride-containing catalysts, includingNi-boride, showed activity for ODHP. Furthermore, all the testedboron-containing catalysts, including Ni-boride, display highselectivity to propene, with the primary byproduct being ethylene.

Inlet flowrates of the C₃H₈/O₂/N₂ gas mixture past the screenedboron-containing, nitride-containing and V/SiO₂ catalysts were varied toachieve a range of propane conversions. Operating conditions were asfollows: P_(O2)=0.15 atm, P_(C3H8)=0.3 atm, P_(N2)=0.55 atm, T=490° C.About 200 mg of boron- or nitride-containing catalysts 600-710 μm insize were loaded in a 9 mm inner diameter quartz reactor with totalinlet flowrates of 40-140 mL min⁻¹, equivalent to WHSV⁻¹ of 100-300kg-cat s m⁻³. All carbon balances close to within ±5%.

As shown in FIG. 15, the boron-containing catalysts, includingNi-boride, maintained high propene selectivity even at high propaneconversions. In sum, this example provides additional data supportingthe Example 4 conclusion that a variety of boron- and nitride-containingcatalyst can be used to catalyze the oxidative dehydrogenation of shortchain alkanes to corresponding olefins.

Example 7 Selective Oxidative Dehydrogenation of n-butane to 1-buteneand 2-butene Using BNNTs

In this example, we demonstrate BNNT-catalyzed ODH using n-butane as thealkane reactant, resulting in a mixture of alkene products, 1-butene and2-butene. The results demonstrate that the disclosed methods are notlimited to ODH of propane (ODHP), but can instead be generalized to ODHof other alkanes to yield the corresponding alkenes.

In the ODH of n-butane, n-butane is dehydrogenated in the presence ofoxygen to yield a mixture of 1-butene and 2-butene. Water is alsoproduced. As noted previously, ODH produces undesirable byproducts, suchas CO; thus, ODH catalysts demonstrating increased selectivity towardsthe desired alkene products (in this case, the C4 butenes, 1-butene and2-butene) are preferred.

Using the general methods outlined in the previous examples (see, e.g.,Example 1 and Example 5), we assayed the ODH catalytic activity ofBNNTs, using n-butane as the alkane reactant. We determined theresulting ODH % conversion of n-butane and the product selectivities asa function of reaction temperature (FIG. 16, temperatures on x-axis;n-butane conversion shown as black squares with values shown on theright side; selectivities shown as bars with values on the left side; C4is 1-butene plus 2-butene). As seen in FIG. 17, BNNTs show favorableselectivity towards the desired C4 products.

We compared the BNNT n-butane ODH conversion and C4 selectivity datawith the values reported for previously disclosed n-butane ODH catalysts(functionalized carbon nanotubes (p-o-CNT), V/MgAl-Spinel,V/MgAl-Hydrotacalcite, and NiMoO₄). As seen in FIG. 17, BNNT showscomparable selectivity (see solid line) to the most selective previouslyreported n-butane catalysts.

Example 8 Selective Oxidative Dehydrogenation of Isobutane to IsobuteneUsing h-BN and BNNTs

This example illustrates BN- and BNNT-catalyzed ODH using isobutane asthe alkane reactant, resulting in isobutene as the alkene product. Theresults provide additional data demonstrating that the disclosed methodscan be generalized to ODH of a variety of alkanes to yield thecorresponding alkenes.

In the ODH of isobutane, isobutane is dehydrogenated in the presence ofoxygen to yield isobutene. Water is also produced. As noted previously,ODH produces undesirable byproducts, such as CO and CO₂; thus, ODHcatalysts demonstrating increased selectivity towards the desired alkeneproduct (in this case, isobutene) are preferred.

Using the general methods outlined in the previous examples (see, e.g.,Example 1 and Example 5), we assayed the ODH catalytic activity of bothh-BN and BNNTs, along with V/SiO₂, a known isobutene ODH catalyst, usingisobutane as the alkane reactant. Reaction conditions were: WHSV⁻¹:16-48 (kg-cat s mol C₄H₁₀ ⁻¹) [V/SiO₂]; 44-111 (kg-cat s mol C₄H₁₀ ⁻¹)[h-BN]; 4-12 (kg-cat s mol C₄H₁₀ ⁻¹) [BNNT]; T=440° C., P_(O2)=0.1 atm,P_(C4H10)=0.1 atm (balance N₂).

The resulting ODH % conversion of isobutane and the productselectivities for each catalyst are shown in FIG. 18 (catalyst used onx-axis; isobutane conversion shown as black squares with values shown onthe right side; selectivities shown as bars with values on the leftside). As seen in FIG. 18, both BN materials (h-BN and BNNTs) show muchhigher selectivity to olefins than the traditional V/SiO₂ catalyst,which shows an undesirable high selectivity towards CO_(x) (˜40%).

We plotted product selectivity as a function of isobutane conversion forthe three ODH catalysts, and the results are shown in FIG. 19. Again,the results show that both h-BN and BNNT catalysts have higherselectivity for the favored olefin products (including, but not limitedto, isobutene), and lower selectivity towards the undesired CO_(x)products than the conventional catalyst.

Example 9 Oxygen Functionalization of the BN Surface Increases CatalystActivity

In this example, we demonstrate that the ODH-promoting activity of BNcatalysts can be improved by bonding (i.e., functionalizing) oxygen tothe BN surface. The BN surface can be functionalized with oxygen usingone or more of a number of methods known in the art.

One such method is to contact the BN with nitric acid. We refluxed h-BNin concentrated HNO₃ for 2 hours. The resulting oxidized BN material wasrecovered by vacuum filtration and dried in an oven overnight. We theninvestigated the catalytic activity of the resulting oxygenfunctionalized material using the oxidative dehydrogenation of propane(ODHP) reaction, as described generally in the previous examples (see,e.g., Example 5).

As seen in FIG. 20, the oxygen functionalized (HNO₃-treated) h-BN shows˜40% increase in the rate of propane consumption over an untreated h-BNmaterial. XPS data confirms that the treated surface was in factfunctionalized with oxygen. Specifically, the HNO₃-treated h-BN contains3.83% (atom %) surface oxygen, while the untreated h-BN only contains2.51% (atom %) surface oxygen.

In sum, this example demonstrates that the ODH catalytic activity ofboron- and nitride-containing catalyst can be further improved bybonding oxygen to (i.e., functionalizing with oxygen) the catalystsurface.

Example 10 BN Catalyzed Oxidative Dehydrogenation of Ethylbenze

This example illustrates BN-catalyzed ODH using ethylbenzene as thealkyl group-containing reactant, resulting in styrene as thecorresponding alkenyl-group containing product. The results provideadditional data demonstrating that the disclosed methods can begeneralized to ODH of alkyl groups attached to an aromatic ring, toyield the corresponding alkenyl group.

We were able attain a saturated ethylbenzene feed into a quartz reactorby bubbling nitrogen through an ethylbenzene saturator kept heated at50° C. The furnace of the quartz reactor tube could be varied to250-500° C., while the surrounding atmosphere from the quartz reactortube furnace was heated to 160° C. Stainless steel tubing from theliquid saturator to the reactor unit and the reactor unit to the gaschromatograph (GC) was kept heated at 220° C. Nitrogen flow through thesaturator was kept constant at 50 mL min⁻¹, while O₂ flow was keptconstant at 5 mL min⁻¹, to give overall feed concentrations as 9% O₂,2.7% ethylbenzene (balance N₂).

The ethylbenzene conversion and product selectivity are displayed inTable 1, comparing the gas-phase reactions of a blank quartz reactortube (only quartz wool) and a quartz tube containing h-BN. Even at 500°C., ethylbenzene conversion is marginal without h-BN present andincreases to 27% conversion in the presence of h-BN, showing lowselectivity to CO_(x) and high selectivity to all other importantproducts (mostly styrene, benzene, toluene).

TABLE 1 ODH of ethylbenzene activity of a quartz reactor tube with andwithout h-BN Product Selectivity [%] Styrene + Benzene + TemperatureEthylbenzene Toluene + Material [° C.] Conversion [%] others CO₂ COBlank 480 3.8 98.1 0.8 1.1 Tube 500 6.0 97.2 0.5 2.3 h-BN 480 21.0 99.40.2 0.4 500 27.4 97.9 0.4 1.7

Example 11 Oxidative Coupling of Methane Using h-BN

This example illustrates the use of h-BN as catalyst for the oxidativecoupling of methane (OCM) into ethane and ethylene products. The resultsshow that the disclosed methods can be used for other types ofoxidations beyond ODH.

In OCM, two methane molecules are coupled to form ethane and ethylene.During this process, water is also produced. The activation of methanerequires significantly higher temperatures than ODH, typically above700° C. These high temperatures lead to the over oxidation of reactionproducts into CO and CO₂. Thus, catalysts that can show activity (i.e.activating methane) while minimizing over oxidation products aredesirable.

Using similar analytical methods as in the previous examples, we assayedthe catalytic activity of h-BN and compared it with that ofcatalytically inert quartz chips. Any activity observed during thequartz chip experiment was deemed to originate from gas phase methaneactivation. To minimize gas phase reactions, quartz wool was used tofill the void space past the catalyst bed. The reaction conditions were:WHSV-1=9-14 (kg-cat s mol CH₄ ⁻¹); T=750° C., 770° C.; P_(O2)=0.20 atm,P_(CH4)=0.4 atm (balance N₂).

The resulting OCM % conversion and selectivity towards coupling products(i.e. ethane and ethene) and COx products are shown in Table 2. At sameflow rates and temperatures, the h-BN catalyst shows an increase inmethane conversion of up to 55% when compared to the activity observedwith the quartz chips. The h-BN catalyst's higher methane activationability leads to a slightly lower C2 selectivity due to the overoxidation of the ethane and ethylene products. Despite this loss ofselectivity, the overall C2 yields are higher than with the quartzchips.

TABLE 2 OCM activity of h-BN and inert quartz chips Total ProductTemperature Flow Conversion Selectivity [%] C₂H₄/C₂H₆ Material [° C.][mL/min] [%] C₂ CO CO₂ Ratio Quartz Chips 750 80 5.5 49.0 48.9 1.1 0.7100 3.7 50.3 48.4 0.8 0.5 120 2.2 52.9 46.1 0.6 0.3 770 80 9.0 47.7 49.51.4 1.1 100 5.8 50.8 47.0 1.1 0.8 120 4.1 52.9 45.4 0.9 0.6 h-BN 750 8013.2 40.1 57.0 1.7 1.2 100 8.2 44.5 53.4 1.1 0.8 120 4.8 44.9 53.7 0.70.5 770 80 20.1 37.9 58.7 2.3 1.6 100 12.6 43.3 54.2 1.3 1.2 120 8.546.6 51.4 0.9 0.9

The invention is not limited to the embodiments set forth in thisdisclosure for illustration, but includes everything that is within thescope of the claims. Furthermore, all documents cited in this disclosureare hereby incorporated by reference in their entirety and for allpurposes as if fully set forth in this disclosure.

We claim:
 1. A method of making one or more desired chemical products,comprising contacting a heterogeneous catalyst comprising a boronnitride that is functionalized with an O₂ moiety (—O—O—) with oxygen andone or more liquid or gaseous reactants, whereby the heterogeneouscatalyst catalyzes the oxidative dehydrogenation (ODH) of the one ormore liquid or gaseous reactants or oxidative coupling of methane (OCM)to form the one or more desired chemical products.
 2. The method ofclaim 1, wherein the O₂ moiety is covalently bonded to a boron atom anda nitrogen atom of the boron nitride, forming a >B—O—O—N< moiety.
 3. Themethod of claim 2, wherein the >B—O—O—N< moiety is at the surface of theboron nitride.
 4. The method of claim 3, wherein the >B—O—O—N< moietyoccurs at an armchair edge of the boron nitride.
 5. The method of claim3, wherein the >B—O—O—N< moiety acts as the catalytic active site. 6.The method of claim 5, wherein the heterogeneous catalyst catalyzes ODH.7. The method of claim 1, wherein: (a) the heterogeneous catalystcatalyzes the oxidative dehydrogenation (ODH) of the one or more liquidor gaseous reactants; (b) the one or more liquid or gaseous reactantsinclude an alkane or a hydrocarbon comprising an alkyl group; and (c)the one or more desired chemical products include one or more olefins orone or more hydrocarbons comprising an alkenyl group.
 8. The method ofclaim 1, wherein the one or more liquid or gaseous reactants includemethane, the heterogeneous catalyst catalyzes the oxidative coupling ofmethane, and the one or more desired chemical products include ethaneand/or ethylene.
 9. A method of making one or more desired chemicalproducts that include one or more olefins or one or more hydrocarbonscomprising an alkenyl group; the method comprising contacting aheterogeneous catalyst comprising a boron nitride that is functionalizedwith an O₂ moiety (—O—O—) with oxygen and one or more liquid or gaseousreactants that include an alkane or a hydrocarbon comprising an alkylgroup; whereby the heterogeneous catalyst catalyzes the oxidativedehydrogenation (ODH) of the one or more liquid or gaseous reactants toform the one or more desired chemical products.
 10. The method of claim9, wherein the O₂ moiety is covalently bonded to a boron atom and anitrogen atom of the boron nitride, forming a >B—O—O—N< moiety.
 11. Themethod of claim 10, wherein the >B—O—O—N< moiety is at the surface ofthe boron nitride.
 12. The method of claim 11, wherein the >B—O—O—N<moiety occurs at an armchair edge of the boron nitride.
 13. The methodof claim 11, wherein the >B—O—O—N< moiety acts as the catalytic activesite.
 14. The method of claim 9, wherein the ODH catalyzed by theheterogeneous catalyst is not zero order with respect to oxygen.
 15. Themethod of claim 9, wherein the ODH catalyzed by the heterogeneouscatalyst is second order with respect to the one or more liquid orgaseous reactants.
 16. The method of claim 9, wherein the one or moreliquid or gaseous reactants include a C₃-C₅ n-alkane, a C₃-C₅iso-alkane, or ethylbenzene, and wherein the one or more desiredchemical products include a C₃-C₅ n-alkene, a C₃-C₅ iso-alkene, a C₄-C₅alkadiene or ethylbenzene.
 17. The method of claim 16, wherein the oneor more desired chemical products further include ethylene.
 18. Themethod of claim 16, wherein the one or more liquid or gaseous reactantsare selected from the group consisting of propane, n-butane, isobutaneand ethylbenzene, and wherein the one or more desired chemical productsare selected from the group consisting of propene, isobutene, 1-butene,2-butene, butadiene and styrene.
 19. The method of claim 9, wherein theoxygen and one or more liquid or gaseous reactants are in a reactantstream that is contacted with the heterogeneous catalyst, and whereinthe reactant stream includes from 0% to 70% nitrogen by volume.